Automatic circuit breaker



R. T. CASEY AUTOMATIC CIRCUIT BREAKER Feb. 26, 1957 Filed Jan. 51, 1955His Attarney m n Q 2 h i\ /1 r 1.

United States Patent AUTOMATIC CIRCUIT BREAKER Robert T. Casey,Southington, Conn., assignor to General Electric Company, a corporationof New York Application January 31, 1955, Serial No. 484,926

11 Claims. (Cl. 200-116) My invention relates to automatic electriccircuit breakers and, more particularly, to small air circuit breakersof the type used for control of light and power circuits in residentialelectrical systems.

One object of my invention is to provide such a circuit breaker in whichthe current responsive element may be calibrated or adjusted prior toits assembly relative to other components of the circuit breaker, thusfacilitating manufacture, assembly and adjustment of the circuitbreaker.

Another object of my invention is to provide such a circuit breaker inwhich the current responsive element is also used as the switchingmember, thereby reducing the number or" parts required.

A further object of my invention is to provide a circuit breakerutilizing a thermal current-responsive element comprising a bimetallicstrip, wherein the bimetallic strip has an inherent electromagneticassisting action.

A still further object of my invention is to provide a circuit breakerhaving a mechanism adapted to utilize portions of the casing walls so asto permit reduction in the number of mechanical parts required.

In general, in accordance with the important features of the invention Iprovide a circuit breaker comprising an elongated U-shaped strip ofbimetallic material having a releasable trip member slidably supportedon one leg thereof. A latch member is carried by the other leg adjacentthe open end of the U and the trip member is normally latched thereonbut is released when the outer ends of the U-shaped strip deflect awayfromeach other upon heating. Upon its release the' trip'member engagesspecially provided cam surfaces carried by the casing and is deflectedthereby to cause opening of the contacts of the breaker. I

My invention will be more readily understood from the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out in the appended claims.

Figure 1 is a side elevation view of a circuit breaker embodying myinvention, the casing being shown partially in section, and themechanism being shown in the normal on condition.

Figure 2 is a view similar to Figure l, the mechanism being shown in theofi condition.

Figure 3 is a view similar to Figure 1, the mechanism being shown in thetripped condition, the handle being unrestrained and having moved to atrip-indicating position.

Figure 4 is an exploded view in perspective of the essential movingparts of the circuit breaker of Figure 1.

Referring now to the drawing, 1 have shown my invention as embodied in acircuit breaker comprising a generally rectangular open-sided insulatingcasing 1 adapted to be closed by a suitable side cover (not shown) whichmay be retained by suitable means such as by screws or rivets passingthrough openings 2. Terminals 3 and 4 are provided for connecting thecircuit breaker in acircuit to be controlled, the terminal S-normzillybeing connected to a line or source of power, and the terminal 4normally being connected to a load or power consuming device. The lineand load terminals 3 and 4 are preferably formed of conductive stripsformed as shown and set into suitable recesses in the casing 1. The lineterminal 3 is provided with a relatively stationary or line contact 5. Amovable or switching contact 6 is supported on one end of a generallyU-shaped bimetallic switching member 7. The bimetallic member 7 ispivotally supported adjacent its bight in the casing 1 by bearingsurfaces of supporting bosses comprising cylindrical boss 8 and thearcuate boss 9. The other end of the bimetallic strip 7 has attachedthereto one end of the flexible braid 10, the other end of which isconnected to the load terminal 4. The circuit through the circuitbreaker when in the closed position may, therefore, be traced asfollows-from a source of power (not shown) to line terminal 3, to linecontact 5, to switching contact 6, to bimetallic strip 7, to flexiblebraid 10, to load terminal 4, to power consuming device (not shown).

The bimetallic strip member 7 and its switching contact 6 are adapted tobe moved from the on or closedcircuit position of Figure 1 to the off oropen-circuit position of Figure 2 and vice versa with a snap action, andalso to be moved to the automatically opened or tripped" position ofFigure 3 by operating mechanism to be described. An operating handle 11of insulating material is provided having a manually engageable portion12 and arcuate side flange portions 13 and 14 adapted to ride incorresponding arcuate tracks 15 in the inner surfaces of the side wallsof the casing 1. The handle 11 is further provided with a hook-eye 16which may be screwed or molded into the handle 11 and which serves as ananchor for the upper end of tension spring 17.

A releasable trip member 18 is slidably supported on one leg of theU-shaped bimetallic strip 7. As may be seen more easily from Figure 4the trip member 18 comprises a rectangular sleeve portion 19, a hook orlatch portion 20, and a tongue portion 21 having a hole 22 thereinthrough which the lower end of the tension spring 17 is adapted to pass.Trip member 18 also has oppositely-directed cylindrical lug portions 23which serve to mount the flat cam members 24 pivotally thereon in amanner to be described. A latch screw or calibrating screw 25 is mountedin threaded engagement in the tapped hole 26 in the opposite leg of thestrip 7, and normally engages and restrains the releasable trip member18 from upward movement. It will be appreciated that although theengagement of calibrating screw 25 and trip member 18 provide a currentpath which is electrically in parallel with bimetal 7 such current isrelatively small due to the relatively high resistance of this parallelpath. In any event the amount of current passing through bimetal 7always varies directly with the total current through the breaker and,therefore, the function of bimetal 7 as a current-responsive element isnot impaired by such paral-lel path.

It will be seen that so long as the releasable trip member 18 is held bycalibrating screw 25 in the lower position as shown in Figure l, thetension spring 17 may be used to exert force on the trip member 18 inthe direction indicated in Figure l tending to move the bimetallicmember 7 oounterclockwise and into engagement with the stationarycontact. When the handle member 11 is moved to the left, as shown inFigure 2, the line of action of the spring 17 crosses the pivotal axisof the bimetallic strip 7 and thereafter biases it in a clockwisedirection to the open-circuit position and against a suitable stop inthe casing 1 such as boss 36.

The central portion of the bimetallic member 7 is cut away, leaving twogenerally parallel spaced-apart portions 27 having a space between themwhich provides clearance for the tension spring 17. The height of thebosses 8 and 9 is made about equal to the width of the side portions 27,and these bosses therefore do not project into the central space betweenthese side portions.

For the purpose of cooperating with the releasable member 18 in causingthe parts to move to the tripped position, I provide elongated bosses28, integral with the opposite side walls of the casing 1 and having camsurfaces 28 (only one shown) for cooperation with the cam surfaces 29,the releasable member 18 is provided with cam follower shoulder portions29.

The bimetallic strip member 7 is arranged so that upon being heated bythe current passing therethrough, it deflects outwardly, so as to moveits end portions away from each other. When this action occurs to apredetermined extent, the latch portion 20 of the releasable member 18becomes disengaged from the tip of the calibrating screw and thereleasable member 18 is thereupon moved upwardly along the arm of thebimetallic strip 7 by the tension spring 17. When this movement hasproceeded only a very short distance, however, the cam follower surfaces29 of the releasable member 18 engage the cam surfaces 28, andridetherealong to the position shown in Figure 3. The action of the camfollower surfaces 29 in riding along the cam surfaces 28, as described,is such as to cause the releasable member 18 to move to the left asindicated during the course of its movement upwardly, under theinfluence of the tension spring 17. Thus it will be observed thatalthough the direction of bias of the tension spring 17 upon thereleasable member 18 is such that in the normal on position it is biasedtoward the relatively stationary contact 5, upon release of the latch 29from the calibrating screw 25 the releasable member is moved along apath which becomes increasingly remote from the relatively stationarycontact 5, thereby moving the bimetallic member 7 to the open-circuitposition. This motion takes place regardless of the manual retention ofthe handle member 11 in the on position.

During the course of movement of the releasable member 18 from the onposition of Figure 1 to the tripped position of Figure 3, the over-alllength of the tension spring '17 becomes shortened, but its direction isalso changed relative to the casing, so that it crosses the'center lineof the arcuate tracks 15 and thereafter biases the handle 11 toward theopen position. By this means, the handle is moved to the midortrip-indicating position in which position it is restrained in a mannerto be described.

In order to reset the releasable member 18 so that the latch portion 20is once again in engagement with the calibrating screw 25, it isnecessary to move the releasable member 13 downwardly along the leg ofthe bimetallic strip 7. In accordance with my invention, I provide meanswhereby this may be done while the handle 11 is moved from thetripindicating or mid position of Figure 3 back to the open-circuit orreset position of Figure 2. For this purpose I provide a cam member 29,preferably integral with the handle member 11 and having a sloping camsurface 39, and elongated bosses 31 (only one shown) to the innersurface of the opposite side walls of the casing 1 and having camsurfaces 32. I further provide flat cam follower members or pushers 24,each having two openings 33 and 34 therein. The cam follower pushermembers 24 are pivotally supported on cylindrical lugs 23 on the tongueportion 21 of the releasable trip member. The enlarged openings 34 inthe cam follower members 24 provide clearance around the projectingbosses 8 and 9 during the course of the various movements of the members24.

7 and the inner side walls of the casing, and their motion is limited ina flatwise direction by the bosses 8 and 9.

The cam follower members 24 are loosely trapped in place between theedges of the bimetallic strip 4 upwardly along the leg of the bimetallicmember 7, the cam members 24 also are moved upwardly and to the positionof Figure 3, in which position they limit the return movement of thehandle member 11 because of the engagement of the cam member 29 with thecam surfaces 35. In order to reset the trip member 18, the handle member11 is moved from the midor trip-indicating position of Figure 3 to theextreme left or reset position :of Figure 2. During this movement thecam surface 30 of cam 29 rides along the rounded cam follower surfaces35 of the cam member 24 forcing the cam follower members 24 to theextreme downward or relatched position. During this resetting movementthe cam follower members also ride along and are guided by the camsurface 32 of the elongated boss 31. The action of the cam surfaces 30and 32 on the cam member 24 is a cooperative one and may be termed asqueeze out action comparable to that by which an orange pip is ejectedwhen squeezed between the fingers. It will be appreciated, however, thatthis resetting action takes place against the bias of tension spring 17and stretches the spring 17 to its origin-a1 length.

The release point of the releasable trip member 18 from the calibratingscrew 25 is dependent only upon the spacing between these two members,which in turn is determined by the spacing between the outer ends of thebimetallic strip 7. This spacing is independent of dimensionalvariations in the casing 1 and may, therefore, be preset before thebimetallic strip 7 is assembled into the casing 1.

Since the current in one leg of the strip 7 is traveling in a directionopposite to that in the closely-spaced parallel leg, there will be atendency of these portions of the strip 7 to repel each other due to theaction of the magnetic fields associated with the currents. While thisforce is negligible with normal current values, on high short-circuitcurrents the force is such as to cause an instantaneous or magnetictripping action which supplements the slower thermal tripping action ofthe strip 7.

While I have shown a particular embodiment of my invention, it will beunderstood that I do not wish to be limited thereto since manymodifications thereof may be made. I, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A circuit breaker comprising a generally U-shaped bimetallic strip, areleasable trip member carried by one leg of said bimetallic strip andbiased for movement relative to said leg to cause automatic opening ofsaid circuit breaker, a latch projection carried by the other leg ofsaid bimetallic strip and normally restraining said releasable tripmember from said movement, said bimetallic strip being arranged so thatits legs deflect out wardly upon heating so as to cause release of saidreleasable trip member from said latch projection.

2. A circuit breaker as set forth in claim 1 also comprising a pair ofterminals and means for connecting said bilnetal strip electrically incircuit with said terminals.

3. A circuit breaker comprising a generally U-shaped bimetallic strip, areleasable trip member slid-ably carried by one leg of said bimetallicstrip, a latch projection carried by the other leg of said bimetallicstrip and normally restraining said releasable trip member, saidbimetallic strip being arranged so that its legs deflect outwardly uponheating so as to cause release of said re leasable trip member from saidlatch projection, said latch projection being carried adjacent the freeend of said one leg of the bimetallic member and said breaker alsocomprising spring means biasing said trip member for movement toward thebight portion of said bimetallic member.

4. A circuit-breaker comprising at least two relatively movablecontacts, a generally U-shaped bimetallic strip pivotally supportedadjacent its bight portion and movable between openand closed-circuitpositions and operatively connected to one of said relatively movablecontacts, a releasable trip member slidably carried by one leg of saidbimetallic strip, a latch projection carried by the other leg of saidbimetallic strip and releasably restraining said trip member, saidbimetallic strip being arranged so that its legs deflect outwardly uponheating so as to cause release of said trip member from said latchprojection.

5. A circuit breaker comprising an insulating casing, a pair of contactsmovable relative to one another, a generally U-shaped elongatedbimetallic strip member pivotally supported adjacent the bight thereofin said casing, said bimetallic strip member and one of said contactsbeing movable together between on and oif positions, a releasable tripmember slidably carried by one leg of said U-shaped bimetallic strip andhaving a latch portion thereon, a latch projection carried by theopposite leg of said bimetallic strip adapted to engage and restrainsaid latch portion of said releasable trip memher, and means operativeupon the release of said releasable trip member from said latchprojection to cause opening movement of said contacts.

6. A circuit breaker as set forth in claim 5 and also comprising a pairof terminals for connecting said circuit breaker in an electric circuitand means for connecting the leg portions of the bimetallic stripelectrically in series with each other and between one of the relativelymovable contacts and one of said terminals whereby current in saidcircuit passes through said leg portions in opposite directions.

7. A circuit breaker comprising an insulating casing, a relativelystationary contact, a relatively movable contact, operating means formoving said relatively movable contact between openand closed-circuitpositions, said operating means including a manually operable handle anda tension spring having one end thereof connected to said handle andhaving the other end thereof normally remote from said handle, areleasable member releasable upon the occurrence of predeterminedcurrent conditions in said circuit breaker to cause automatic opening ofsaid contacts, the remote end of said tension spring being connected tosaid releasable member, said remote end of said spring moving towardsaid handle member upon release of said releasable means, and means forreturning said releasable member and said remote end of said spring tonormal position, said means comprising a stationary cam surface carriedby said insulating casing, a movable cam surface carried by said handlemember, said movable and said stationary cam surfaces being inclinedtoward each other at an angle less than 90, and a movable cam followermember operatively connected to said releasable member and adapted to bemoved by the cooperative action of said stationary cam surface and saidmovable cam surface as said operative handle is returned toward itsopen-circuit position.

8. A circuit breaker comprising an insulating casing, a stationarycontact, a cooperable movable contact, a movable switch member formoving said movable contact between on and off positions, a firstterminal connected to said stationary contact, a second terminalconnected to said movable contact, manually operable means for movingsaid switch member between said on" and off positions, said manuallyoperable means comprising a handle of insulating material, meanssupporting said insulating handle for arcuate movement in said casing,trip means releasable to cause automatic opening movement of said switchmember when in said on position, said trip means including a latchingportion norrnally engaged and held by a current responsive latch memberand a second portion movable upon release of said latching portion in adirection toward said handle, and resetting means for manually returningsaid latching portion to its normal latched position, said resettingmeans comprising a cam follower member connected to said second portionof said trip means and a cooperating cam carried by said insulatinghandle.

9. A circuit breaker comprising an insulating casing, a pair of contactscarried by said casing, at least one of said contacts being movablebetween open and closed positions, a manually operable member carried bysaid casing and movable between on and off positions, a switch memberpivotally mounted in said casing and adapted to move said one of saidcontacts between said open and closed positions, a releasable tripmember carried by said switch member, a tension spring interconnectingsaid manually operable member and said trip member, said tension springpassing across the pivot point of said switch member as said manuallyoperable member is moved from on to off position to provide a snapaction, said tension spring biasing said trip member for movement towardthe pivot point of said switch member when said switching member is insaid on position, current responsive latching means for preventing saidmovement of said trip member, a relatively stationary cam surfacecarried by said casing, said trip member being adapted to engage saidcam surface upon its release from said latching means and to have itsmovement thereafter directed thereby so as to carry said switch membertoward open position and to carry said tension spring across the pivotof said switch member.

10. A circuit breaker as set forth in claim 9 wherein the switch membercomprises a generally U-shaped strip of bimetallic material pivotedadjacent the bight portion thereof.

11. A circuit breaker as set forth in claim 10 wherein the trip membercomprises a sleeve slidable along one leg of the U-shaped bimetallicmember.

References Cited in the file of this patent UNITED STATES PATENTS2,070,305 Jennings Feb. 9, 1937 2,216,748 Lindemann Oct. 8, 19402,247,193 Frank June 24, 1941 2,320,356 Frank et al. June 1, 19432,400,984 Dyer et a1 May 28, 1946 2,602,129 Valverde July 1, 19522,618,720 Besag et al. Nov. 18, 1952 2,685,011 Boller et al July 27,1954 2,692,929 Ericson Oct. 26, 1954 2,701,829 Krieger Feb. 8, 1955

